9 replies to this topic

[ojannen]

I just picked up a mini shell and I am planning on building it into a road/race car in the southeastern US.  I am working on planning the build now and I have some questions about tires which are a little different than the normal questions here.  I am planning on running a couple different types of time trial events and hopefully just changing tires and suspension setup between them.

 

My primary interested is autocross.  It is similar to a hill climb but on a temporary course.  Speeds rarely exceed 65 mph and rarely go below 25 mph after the start.  Shifting out of second gear is rare in most cars.  Here is an example in my modern mini on street tires.  A classic mini with a built 1275 engine fits nicely into the E Prepared class.  Most of the class is old Honda Civics and CRXs on 10" wide Avon bias ply qualifying slicks.  How wide of a tire can reasonably go on stock suspension geometry?  At what point does power steering become helpful?

 

I am also interested in US style rallycross.  This is considerably different that rallycross in the UK.  They courses try to feel like a scaled down version of a rally stage that is smooth enough to run in a car on stock suspension.  Here is an example in a nearly stock BMW 3 series.  Generally people use gravel or mud rally tires.  I have found some good 10" and 12" options looking at autograss tires.  I am having trouble finding a mud tire that fits the mini.  This is the default mud tire for rallycross.  The Maxsport Hakka 2 is the closest tire I have found but it only comes in 155/70r13 which is a little to large for a mini.  Are there any other options?

 

I have not yet attended but I am taking a serious look at the Optima Ultimate Streetcar Challenge.  The rules are designed for American muscle cars but they don't include any minimum weights.  The mini could have an advantage by weighing 2000lbs less than every other car.  The competition includes an autocross, road course, brake test, and a road rally.  Competitors have to use the same set of tires for every event and the tires must be 200 treadwear or above.  The standard tires for the event are the Bridgestone RE-71 and the BF Goodrich Rival-S.  The smallest size they come in is 15".  I cannot find any tires that fit the mini and have a 200 treadwear rating.  The Yokohama A008 looks like it is close but I can't find a treadwear rating on it.  The yokohama A539 is a 300 treadwear tire and it is probably seconds slower on an autocross course.

[Allrounder]

Both events are similar to what I use my mini for. Autosolos are based on your autocross though only on a 200m x 200m area. I use a539 on 13 sport pack wheels as were restricted to standard road tyres. The only issue I find with the is on a hot day and pushed hard they can over heat and lose grip.

If your sending a lot of time in 2nd gear and depending on how much power youve got then Id life the gear set as l have broken laygears. And power steer will help especially with bigger stickyer tyres.
https://youtu.be/B8HqZrLhSaI

Same car for our autocross but with max sport RB1 tyres on 12 rims and raises suspension.
https://youtu.be/-NC6I0HK2ro

Think the most important thing is to get the setup right for your driving style.

Edited by Allrounder, 06 May 2018 - 08:49 AM.

[nicklouse]

wheel sizes. note the Sportpack cars had steering rack travel reducers fitted.

 

I would go to big wheels. i would look at 10s and look at some Hoosier hillclimb/sprint tyres of the asphalt and for the dirt something like the Dunlop SP44 Weathermaster

[Magneto]

Go here for tires, they have every type you need and even in 10" sizes. They have asphalt racing tires and dirt tires and the prices are reasonable.....plus they're in Texas so shipping is reasonable.

 

https://americanraceronline.com/

 

Also, for a "local" Classic Mini site, go to Restoration Mini dot com, good guys and very knowledgeable.

Edited by Magneto, 06 May 2018 - 11:49 PM.

[nicklouse]

cant see any 10s there other than width

[ojannen]

Thanks for the information.  The auto solo looks pretty fun.  Do you ever run on old airport runways?  We have a bunch left over from World War 2 here.  They don't allow for as many sweepers but you can still end up with an interesting course:

 

I have never seen UK autocross before.  I thought the closest thing to US rallycross was autograss.  It is almost exactly what we are doing, just with one car on course at a time.  Do you normally run rubber cones or coil springs on the dirt?  I like the idea of a constant rate spring on dirt to keep things consistent but I have never run something as light as a mini.  Is there much camber change when you change the ride height?

 

How does a gravel tire like the Maxsport RB1 differ from an autograss tire like the Maxsport Hakka?  Is there a difference in sidewall stiffness or compound?

 

For autocross, just about everyone uses Hoosier R25 slicks or the equivalent Avon qualifying tire.  The Avons are known to take a little longer to heat up and are used more often by cars with two drivers in the same class.  Hoosier A7s are legal too but are generally thought to be a bit slower.  For the mini, my choice is going to be based on shipping costs.  It is tough to get 10" or 12" tires in the US.  My wife and I both compete so we should be able to get anything up to temperature.

 

Where do you go for 10x7 or 10x8 wheels?  I found some expensive 3 piece wheels, some ATV wheels, and not much else.

[nicklouse]

like i said Hoosier slicks for 10s i forget what i used to run

 

constant rate springs on a Mini. good luck unless you like welding. there is not a kit available for the Mini that either gives you a constant rate spring on the suspension. you end up with a falling rate or a failing car. the coil over kits have the springs in the only space they can and it is wrong. and the coils that replace the rubber do not have enough travel and go coil bound.

 

so rubber cones with HiLos.

 

wide tens have a chat with Force racing  http://www.force-rac...cing-10-wheels/ dont go to wide or you will have issues.

[ojannen]

I am aware these questions are fairly basic.  I am happy to use rubber cones but I want a better understanding of why coils or even coilover setups don't work.

 

How much suspension travel is lost when going from cones to coil springs?

If the coils are binding, why isn't the solution to run stiffer springs?

How are the springs on the coilover kits wrong?  Still too short?

[nicklouse]

for coil overs to work you need to move the top mounts inside the inner wings. look at any space frame mini that has to use mini suspension but runs coil overs. the top mount is nowhere near the one in the kits as they dont want a falling rate spring. they want a rising rate one so the suspension gets stiffer in roll means you dont have to run a stupid hard spring that loses loads of grip for you on the small bumps

 

running stiffer springs does not help in fact it makes it worse as you have even less space for them. oh see above re harder springs.

 

have a read up on suspension design rates. and also spring rates and what happens when you incline a spring to the input force.

 

 some pictures for you

yes i am running soft springs with a fair bit of preload and next to no travel. and their is a reason for that.

 

then onto the rubber replacement springs

 

[Magneto]

I'll get you a link to the10's

 

https://americanrace...print-atv-dirt/

Edited by Magneto, 08 May 2018 - 01:26 AM.