185 or 205?

[mont7]

I have a 1998 Caterham DeDion with a 1700 Crossflow (approx. 150 hp on a good day, head work, 244 cam). Recently purchased a used set of 13"X6" Panasports to use for both Autocross and Track days. Run about 5-10 autocross events, and about 3 track days a year. Novice driver for both types of events, and will drive to all events (up to about 300 - 350 miles for the track days.) I'm more interested in having the right tires for the track days rather than autocross.

I've settled on the the Toyo RA1 as a good compromise tire. I was originally planning on just putting 205 X 60 all around, but now am wondering if that is too much tire, at least from the track day standpoint? Options under consideration are:

185 x 60 front and rear
185 x 60 front, 205 x 60 rear
205 x 60 front and rear

All input is appreciated. Thanks.

Steve

[moosetestbestanden]

The 185/60 shows a 7.4" width & 21.7" diameter, the 205/60 shows 8.2" width & 22.7" diameter.

For comparison purposes, the Avon ACB 10 in a 7.0/21-13 (front) is 7.6 & 20.7 and the 8.0/22-13 (rear) is 8.7 & 22.1.

So, if you chose to go w/ the 185/60 front and 205/60 rear you would get (pretty) close to the dimensions of a set of the Caterham specific Avons. Don't know a thing about Toyos otherwise, except that a number of Lotus 7 Club members have a favorable view of the Toyo R888s. I can't seem to find any reference for those on this side of the puddle.

[Roll a 7]

I think Kumho V710s are the best tires out there, but they are available in only one 13" size and you would NOT want to drive to the track on them. I use them on each corner and would not settle for a lesser tire after using them.

[Boxologist]

the r888 are not US DOT approved (yet?). so they are real grey market. i'm not sure if teh cr500 is either.

[mont7]

Chris - Interesting about the comparison to the ACB10's. Didn't realize that Caterham recommended different sizes front/rear.

It's really Blatchat that caused my confusion. I found numerous threads about the "correct" tire (tyre?) sizes, with lots of posts about the tire size (width really) to HP ratio. But they also discuss at length the issue of increased understeer with wider rears. Just to compound my fears, I added an LSD over the winter, which per Blatchat also contributes to understeer.

Having sad all that, the rims came with some pretty worn 215/50 Kumho V700's, which I've used at the first two autocross events (it's only about a 15 mile drive). They didn't seem like too much tire at the autocross, and there seems to be less understeer.

Then there is the rim width question. Again, on Blatchat the impression I get is that it's questionable to put 205/60's on 6" rims. Lots of people seem to put them on 7" and 8" rims. Yet the Toyo site states that 6" is the recommended rim.

I spoke to a midwest tire dealer yesterday (Frisby Race tire outside Chicago), and he said that although they announced that the R888 was coming to the US at SEMA, he didn't think they would show up until the end of this year at the earliest.

So, another request for opinions/experience. Will the wider rears really cause a large/noticeable/annoying increase in understeer? Assume it would be most noticeable during slower corners?


Steve

[moosetestbestanden]

Tire... er... tyres:D are always a major, um, discussion point, so confusion will always reign. Remember that a lot of the fellas on BC don't like to spend money so that's always a factor in their "favorite tyre" chatting.

My approach has been to look at what CC racing requires and follow that, mostly because there's a sizable body of information regarding general setup (camber, toe, corner weights, ride height etc.) that combined w/ the tyre will provide a mechanical hack like me a good baseline to get pretty neutral handling. It's working. The (still stillborn, for lack of participants:() NASA Caterhams Challenge settled on ACB10s for reasons of equality and (semi) reasonable cost, and fwiw I concur - it seems wise for the same reason I mention above. That's why I offered up the size comparison.

Not being expert in such things, I would think that the 205/60 on a 6" rim might lead to more sidewall flex (I think?) but at least the dimensions of the tires you're looking at are close, as I mentioned. I am assuming that the RA1 is a radial tire.

I have a set of Avon CR500s (edit: a radial tyre) sitting in the garage that are basically new (and that I'll likely never use again). When I get home from work today I'll get the sizes and then compare dimensions w/ the other 2 to see how all 3 compare, unless someone can beat me to it today.

[mont7]

Chris - Be interesting to see the width comparison on the CR500's. Again per Blatchat, the Avons are apparently considerably wider than their stated width. A recent post included the following link:

http://homepage.ntlworld.com/ben_marriott/misc/500vs21R.jpg

which shows a 175/55 CR500 as wider than a 185/60 Yoko A021R.

Per the Toyo site, the inflated width of the 185/60 RA1 is 7.4 inches, and the 205/60 is 8.2 inches.

Not sure I'm making progress with this, and want/need the tires for a track day on June 4. Decisions, decisions! Right now I'm leaning toward the 205 in back and the 185 in front, but ask me in 10 minutes and I'll probably give you a different answer.

Steve

[moosetestbestanden]

The CR500s Caterham uses are:

175 55 R13s 20.75" dia. & 7.24" width front
205 55 R13s 21.80" dia. & 9.06 width rear

If you want to stay close to what CC uses then fit the 185s front and 205s rear.

[Boxologist]

r888 pending USA release june 21, 2007. second hand news to me, so take it with a grain of salt.

[Elv15]

It will be interesting to see what sizes of the r888 are offered here in the USA. ..and what the prices are!

I've been running a032's but the fronts are narrower than I would like, 175's. 185/front and 205/rears seem just about right.

[mont7]

It seemed like my decision was going to be made for me, as I couldn't find any 205/60X13's anywhere. But then on Friday a dealer I found (http://www.performance-chassis.com) called back to say that he had them available. Ended up just getting 4. To be honest, didn't want to mess with adjusting the rake. Decided if I don't like it, I'll buy to 185/60's and, since I'll have an extra set of rears, practice donuts.

One dealer I spoke with didn't think the R888 would be here until early 2008. He expects that they will start with 15" - wasn't real optimistic about them bringing 13" in.

Steve

[Roll a 7]

Tire dealers tend to want to sell you what they have in inventory.