Creepy Krawlers
Moderator: Committee
Re: Creepy Krawlers
That thing is awesome! Far too many expensive thoughts bouncing around my head at the moment!
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gwagensteve
- Financial Member
- Posts: 2163
- Joined: Mon 13 Aug, 2007 5:20 pm
Re: Creepy Krawlers
There's a lot of complex stuff going on in this thread, and a lot of it relates to the, sort of, "philosophy" of building a car for our conditions. I'll weigh in with some thoughts, but it might start getting a bit off track. I'll try and break it up into sections so it's easier to follow.
Obviously, these are just my thoughts - others will disagree, and build whatever takes your fancy - you need to settle on a wheel/tyre combination that floats your boat, regardless, to some extent, that their might be something that might work better.
Firstly, and this is in no way a criticism Leigh, but comparing performance between cars from this year's tour is really fraught with difficulty. The dryness was such a dominant factor this year that all the bigger cars were really just taking silly lines and we weren't really working for anything. The key issue was that the conditions didn't really allow ground pressure and wheelbase (much) to come into play. These are two issues I'm keen to talk about in relation to tyre choice because they're critical to consider at this point. With some more moisture this year, there would have been some really interesting comparisons to be had.
I also don't want to take anything away from Luke's achievement by getting his car on tour, but I haven't seen it in enough conditions to really assess what it can do. Luke and I were discussing its "squareness" on the tour and how that might be a bit of an issue going forwards - his original plan was to build LWB and I think that's likely to work much better.
Anyways, onto ground pressure and wheelbase.
There's been lots of discussion over the years (mostly related to Jeeps) about optimum wheelbase vs tyre size. Effectively, when you step up in tyre size, it's like you're making your car shorter. In some terrain, that doesn't make any difference, but if you need to get on the power or are working big ledges, a longer wheelbase make the car much easier to keep pointing up the track. Obviously, there are other advantages on ledges, for example, where more wheelbase can span obstacles and limit weight transfer.
As you add width, you also effectively make your car "shorter" in that it becomes more square viewed from above. This also effects the cars directional stability when you're climbing, particularly when its wet - the car will be less responsive to steering and more responsive to changes in the camber of the track.
Obviously, as you add tyre diameter, the cars COG goes up. This can be mitigated side to side by increasing track width, but not so easily front to back. A higher car will weight transfer more on steep climbs. Add in the increased traction from a bigger tyre, and you can see how it's quite easy to get the car to "sit up" on climbs like Greg's car was doing on that ledge.
It sounds like I'm just advocating lots of wheelbase, but I'm not at all, I'm just pointing out that as you increase tyre size, the disadvantages of a very short wheelbase become more apparent, partially because of the increased height, partially because of the increased traction. It might mean that a car on 34's feels more balanced and trustworthy than a car on 36's, even though objectively, the 36's make the car more capable. however, add 6" to the wheelbase and the car on 36's might really start to work and feel good. Some of this is a matter of driving style too. Greg and Mika, for example, like to really, really noodle about and take their time. They can get away with far less wheelbase than someone like Jim or myself who's more inclined to punch it a bit more.
Ground pressure
This is where it's easy to fall out of love with the Krawlers. It's hard to develop ground pressure with a Sierra, they're so light. In summer, ground pressure is pretty irrelevant (that is to say, there's rarely too little ground pressure) . Nobody on this years tour was really hurting for traction regardless of tyre size or pressure. However, in winter, very low ground pressure starts to hurt traction, or at the very least, directional stability. My old 9/34 swampers had probably the most ground pressure of any taller tyre, and as a result on greasy climbs like cockpit creek, I would generally have plenty of traction and directional control. With the Krawlers, once the centre of that tread is packed with mud, the tyre is presenting a big, flat, square surface to the ground and they won't hook up - it's skating about on the surface.
This is obviously where Boggers excel - they generate very high ground pressure even in large sizes because they have so much void. Silverstone Extremes are another really good example of a tyre designed with very high void to generate high ground pressure.
Like every choice, this is a balance. Very high void tyres offer no advantage on rock or in the dry. They also drive poorly on road. To generate higher ground pressure, it's best for a tall high-void tyre to be narrower. Jim's 35 10.5 silverstone extremes are a good example, as are 38 11.5 Boggers.
footprint aspect ratio
By this I mean height to width. To a certain extent, in low traction conditions, a tyre is like a rudder. A short, wide tyre has a very "square" footprint and as such offers little difference in directional control if turned. a tall narrow tyre has an excellent "rudder" effect by offering a long, narrow footprint. This improves drivability a lot. For the same footprint surface area, a narrower footprint also takes less power to turn as it's not presenting a wide face to unbroken ground. This was very noticeable when I went to the Krawlers - I could feel their increased rolling resistance in mud - it really felt like the car was being held back.
Soooo... what you want to get out of your tyres is a really complex web of compromises.
We're running Krawlers because of their rut filling width, soft compound, and excellent carcass construction (for a Radial) they work very well for "noodling" on technical tracks. However, we've traded off directional control on greasy hills and to a certain extent mud performance (although they do quite well)
In some conditions, your 31" mongrels will outperform the Krawlers - I've seen it happen, in conditions when high ground pressure is required.
Boggers, in, say, 35 10.5, would offer really excellent winter performance, but in the dry you won't be as happy- by all accounts they are totally outclassed by more modern tyre designs. Those wide tread blocks don't want to hold edges laterally (like trying to hang on to a bank or rut) and the tyre wants to fold in the middle rather than flex those big blocks. They are also a tyre that's completely optimised for throttle - they were designed as a DOT legal mud drag tyre. It's almost an accident they ended up on trail cars at all - Rick Pewe, Ned Bacon, Mike Flores and Jimmy Nylund did a tyre test on them at Truckhaven hills in California for Fourwheeler magazine when they came out (1995?) and they quite liked their performance, and I think lots of guys tried them off the back of that. This is before almost every modern off road tyre existed though. I've seen some cars running boggers in action, but never really in anything where I'd make a call on their awesomeness. I think they're more a novelty item outside of mud bog competition to be honest.
Good old swampers work really well - the advantage is a huge range of sizes and very proven, versatile performance. Word on the street is that the compound is much harder than newer tyres and this hurts their rock performance, but it seems that LTB's have a softer, more contemporary compound. The advantage of swampers is that you're not locked into one size - you can really play with the size chart to get what you want. Many swamper sizes have been unavailable for some time, but at Wandin I saw a Q78 16 with a recent build date on it, so they look to be in production.
I think the real choice is whether you want to "rut fill" or not. In all honesty I think Q78 15/16 swampers are probably a better all round tyre for us than the krawler, but at 10.5 wide they don't rut fill so side-by-side the Krawler will always look to be superior. Michael is looking to reduce his rim offset to tuck his Q78's in as far as possible to try and work the inside edge of the ruts as a compromise. Likewise, the 35 12.5 LTB is a narrow 12.5, which is bad for rut filling but good for performance otherwise.
How much backspacing can you run?
I have full steering lock with 15X8" 3.75" BS Walkers and 35" Krawlers. I have very light contact between the chassis and the tyre at full lock.
I have 6.25" between the tyre inside edge and the chassis.
By my calcs, a 17X9" 4.5" BS wheel will put the rim edge 0.75" closer to the chassis, but with a 35X12.5" LTB, the tyre section is 1.7" narrower, so the tyre carcass at it widest point is actually 0.85" further away from the chassis. (7.1") That's a pretty good outcome, but I'm not sure if it's really "better" - you're wider inside/inside so less able to grab the inside, and narrower outside/outside so potentially less stable. I guess the advantage is that with a narrower tyre you might be able to get the tyres to tuck better (and you'll have less scrub radius) so the whole car might be able to be a fair bit lower.
Some of this is what's available though. My tyre/wheel combo was second hand and owes me staggeringly little money. I'm willing to compromise a bit on what might be ideal when something close to ideal is available cheap.
The axle debate
I think that switching to off-brand axles is a very double edged sword. It allows a cheap solution to dependable reliability, but it also changes the nature of the car totally. a sierra on hilux/patrol/60 series diffs works quite differently to a sierra still on suzuki axles. I also think its very hard to avoid loosing control and keeping "balance" in the build - it's easy to start looking at 37's... a wheelbase stretch... some coils, and the next thing you have something that's either too capable* or too unusable. (or an unfinished project)
Anyway, that's all stuff to think about. There's no out-and-out right and wrong answers - it's all a matter of compromise, priority and budget.
Steve.
*Excessive capability is a very real problem. It sounds impossible, but we're terrain limited in Vic - as in we're on tracks and not on private property where there's unlimited line choice. It's cool to have to work for it a bit and be part of a group of guys all working for it a bit. If it was possible to build something totally dominant it's actually quite boring to drive. Mick experienced this with Critta, which was basically a tube/comp car by the time it went on its last tour. I like the fact we are limited by what's appropriate to drive on the road too.
Obviously, these are just my thoughts - others will disagree, and build whatever takes your fancy - you need to settle on a wheel/tyre combination that floats your boat, regardless, to some extent, that their might be something that might work better.
Firstly, and this is in no way a criticism Leigh, but comparing performance between cars from this year's tour is really fraught with difficulty. The dryness was such a dominant factor this year that all the bigger cars were really just taking silly lines and we weren't really working for anything. The key issue was that the conditions didn't really allow ground pressure and wheelbase (much) to come into play. These are two issues I'm keen to talk about in relation to tyre choice because they're critical to consider at this point. With some more moisture this year, there would have been some really interesting comparisons to be had.
I also don't want to take anything away from Luke's achievement by getting his car on tour, but I haven't seen it in enough conditions to really assess what it can do. Luke and I were discussing its "squareness" on the tour and how that might be a bit of an issue going forwards - his original plan was to build LWB and I think that's likely to work much better.
Anyways, onto ground pressure and wheelbase.
There's been lots of discussion over the years (mostly related to Jeeps) about optimum wheelbase vs tyre size. Effectively, when you step up in tyre size, it's like you're making your car shorter. In some terrain, that doesn't make any difference, but if you need to get on the power or are working big ledges, a longer wheelbase make the car much easier to keep pointing up the track. Obviously, there are other advantages on ledges, for example, where more wheelbase can span obstacles and limit weight transfer.
As you add width, you also effectively make your car "shorter" in that it becomes more square viewed from above. This also effects the cars directional stability when you're climbing, particularly when its wet - the car will be less responsive to steering and more responsive to changes in the camber of the track.
Obviously, as you add tyre diameter, the cars COG goes up. This can be mitigated side to side by increasing track width, but not so easily front to back. A higher car will weight transfer more on steep climbs. Add in the increased traction from a bigger tyre, and you can see how it's quite easy to get the car to "sit up" on climbs like Greg's car was doing on that ledge.
It sounds like I'm just advocating lots of wheelbase, but I'm not at all, I'm just pointing out that as you increase tyre size, the disadvantages of a very short wheelbase become more apparent, partially because of the increased height, partially because of the increased traction. It might mean that a car on 34's feels more balanced and trustworthy than a car on 36's, even though objectively, the 36's make the car more capable. however, add 6" to the wheelbase and the car on 36's might really start to work and feel good. Some of this is a matter of driving style too. Greg and Mika, for example, like to really, really noodle about and take their time. They can get away with far less wheelbase than someone like Jim or myself who's more inclined to punch it a bit more.
Ground pressure
This is where it's easy to fall out of love with the Krawlers. It's hard to develop ground pressure with a Sierra, they're so light. In summer, ground pressure is pretty irrelevant (that is to say, there's rarely too little ground pressure) . Nobody on this years tour was really hurting for traction regardless of tyre size or pressure. However, in winter, very low ground pressure starts to hurt traction, or at the very least, directional stability. My old 9/34 swampers had probably the most ground pressure of any taller tyre, and as a result on greasy climbs like cockpit creek, I would generally have plenty of traction and directional control. With the Krawlers, once the centre of that tread is packed with mud, the tyre is presenting a big, flat, square surface to the ground and they won't hook up - it's skating about on the surface.
This is obviously where Boggers excel - they generate very high ground pressure even in large sizes because they have so much void. Silverstone Extremes are another really good example of a tyre designed with very high void to generate high ground pressure.
Like every choice, this is a balance. Very high void tyres offer no advantage on rock or in the dry. They also drive poorly on road. To generate higher ground pressure, it's best for a tall high-void tyre to be narrower. Jim's 35 10.5 silverstone extremes are a good example, as are 38 11.5 Boggers.
footprint aspect ratio
By this I mean height to width. To a certain extent, in low traction conditions, a tyre is like a rudder. A short, wide tyre has a very "square" footprint and as such offers little difference in directional control if turned. a tall narrow tyre has an excellent "rudder" effect by offering a long, narrow footprint. This improves drivability a lot. For the same footprint surface area, a narrower footprint also takes less power to turn as it's not presenting a wide face to unbroken ground. This was very noticeable when I went to the Krawlers - I could feel their increased rolling resistance in mud - it really felt like the car was being held back.
Soooo... what you want to get out of your tyres is a really complex web of compromises.
We're running Krawlers because of their rut filling width, soft compound, and excellent carcass construction (for a Radial) they work very well for "noodling" on technical tracks. However, we've traded off directional control on greasy hills and to a certain extent mud performance (although they do quite well)
In some conditions, your 31" mongrels will outperform the Krawlers - I've seen it happen, in conditions when high ground pressure is required.
Boggers, in, say, 35 10.5, would offer really excellent winter performance, but in the dry you won't be as happy- by all accounts they are totally outclassed by more modern tyre designs. Those wide tread blocks don't want to hold edges laterally (like trying to hang on to a bank or rut) and the tyre wants to fold in the middle rather than flex those big blocks. They are also a tyre that's completely optimised for throttle - they were designed as a DOT legal mud drag tyre. It's almost an accident they ended up on trail cars at all - Rick Pewe, Ned Bacon, Mike Flores and Jimmy Nylund did a tyre test on them at Truckhaven hills in California for Fourwheeler magazine when they came out (1995?) and they quite liked their performance, and I think lots of guys tried them off the back of that. This is before almost every modern off road tyre existed though. I've seen some cars running boggers in action, but never really in anything where I'd make a call on their awesomeness. I think they're more a novelty item outside of mud bog competition to be honest.
Good old swampers work really well - the advantage is a huge range of sizes and very proven, versatile performance. Word on the street is that the compound is much harder than newer tyres and this hurts their rock performance, but it seems that LTB's have a softer, more contemporary compound. The advantage of swampers is that you're not locked into one size - you can really play with the size chart to get what you want. Many swamper sizes have been unavailable for some time, but at Wandin I saw a Q78 16 with a recent build date on it, so they look to be in production.
I think the real choice is whether you want to "rut fill" or not. In all honesty I think Q78 15/16 swampers are probably a better all round tyre for us than the krawler, but at 10.5 wide they don't rut fill so side-by-side the Krawler will always look to be superior. Michael is looking to reduce his rim offset to tuck his Q78's in as far as possible to try and work the inside edge of the ruts as a compromise. Likewise, the 35 12.5 LTB is a narrow 12.5, which is bad for rut filling but good for performance otherwise.
How much backspacing can you run?
I have full steering lock with 15X8" 3.75" BS Walkers and 35" Krawlers. I have very light contact between the chassis and the tyre at full lock.
I have 6.25" between the tyre inside edge and the chassis.
By my calcs, a 17X9" 4.5" BS wheel will put the rim edge 0.75" closer to the chassis, but with a 35X12.5" LTB, the tyre section is 1.7" narrower, so the tyre carcass at it widest point is actually 0.85" further away from the chassis. (7.1") That's a pretty good outcome, but I'm not sure if it's really "better" - you're wider inside/inside so less able to grab the inside, and narrower outside/outside so potentially less stable. I guess the advantage is that with a narrower tyre you might be able to get the tyres to tuck better (and you'll have less scrub radius) so the whole car might be able to be a fair bit lower.
Some of this is what's available though. My tyre/wheel combo was second hand and owes me staggeringly little money. I'm willing to compromise a bit on what might be ideal when something close to ideal is available cheap.
The axle debate
I think that switching to off-brand axles is a very double edged sword. It allows a cheap solution to dependable reliability, but it also changes the nature of the car totally. a sierra on hilux/patrol/60 series diffs works quite differently to a sierra still on suzuki axles. I also think its very hard to avoid loosing control and keeping "balance" in the build - it's easy to start looking at 37's... a wheelbase stretch... some coils, and the next thing you have something that's either too capable* or too unusable. (or an unfinished project)
Anyway, that's all stuff to think about. There's no out-and-out right and wrong answers - it's all a matter of compromise, priority and budget.
Steve.
*Excessive capability is a very real problem. It sounds impossible, but we're terrain limited in Vic - as in we're on tracks and not on private property where there's unlimited line choice. It's cool to have to work for it a bit and be part of a group of guys all working for it a bit. If it was possible to build something totally dominant it's actually quite boring to drive. Mick experienced this with Critta, which was basically a tube/comp car by the time it went on its last tour. I like the fact we are limited by what's appropriate to drive on the road too.
michaelpiranha2000 wrote: The rear is in great condition. but has a broken crown wheel and pinon
Re: Creepy Krawlers
Thanks for taking the time on such a detailed response there Steve, lots of good info and points that I'll be taking into consideration while planning my build.
Ultimately I think it will come down to what tyres i can get for a resonable price, as i dont have the budget to spring for new tyres and wheels, and then building the rest of the car around what will work best with what i have.
Really apprieciate all the imput guys, you've given me far to many things to think about!
Ultimately I think it will come down to what tyres i can get for a resonable price, as i dont have the budget to spring for new tyres and wheels, and then building the rest of the car around what will work best with what i have.
Really apprieciate all the imput guys, you've given me far to many things to think about!
Re: Creepy Krawlers
Nice response there Steve.
100% agree on the ground pressure. My Silverstones are ace on muddy and clay tracks. far from being good on rock. The swampers are probably better all round but the Silverstones are great in winter.
A note on the LTB's, the 15" size has a load rating WAY lower than the 16", indicating that the 15" would be the one to go for on a Sierra.
100% agree on the ground pressure. My Silverstones are ace on muddy and clay tracks. far from being good on rock. The swampers are probably better all round but the Silverstones are great in winter.
A note on the LTB's, the 15" size has a load rating WAY lower than the 16", indicating that the 15" would be the one to go for on a Sierra.
Re: Creepy Krawlers
this thread is making me wish there was a 35x13.5 swamper 
the best i can find is a 35x12.5 TSL or a 36x13.5 IROK.
in theory it will fill the ruts, provide good ground pressure, have good sideways traction and bring the shoulder lugs for added climbing goodness.
the best i can find is a 35x12.5 TSL or a 36x13.5 IROK.
in theory it will fill the ruts, provide good ground pressure, have good sideways traction and bring the shoulder lugs for added climbing goodness.
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gwagensteve
- Financial Member
- Posts: 2163
- Joined: Mon 13 Aug, 2007 5:20 pm
Re: Creepy Krawlers
Pretty sure there is a 35x15? Might not still be in production. Iroks are light and voidy, but have very little sidewall lug.
Steve.
Steve.
michaelpiranha2000 wrote: The rear is in great condition. but has a broken crown wheel and pinon
Re: Creepy Krawlers
was never sold on the Irocks. They have BIG voids and not a lot of lug in many of the sizes. The ones we ran when "loaning" NAM's old buggy almost looked like a turf tyre they had such small lugs.
Greg, there's always the "dual wheel" option.
Greg, there's always the "dual wheel" option.