rake and trail questions......

Dave I would really like to thank you for putting all the information out that you do. Last year before the start of the season I bought twiddling knobs and introduction to suspension, I have watched them at least a dozen or so times a piece. That is also another reason why I think I did so well in my first racing year 2008 with a 2003 bike. I would absolutely love to go to one of your seminars but do not have the time or resources currently to fly to California from Fort Wayne, Indiana.

Do you have any sort of articles or guides that would help be better understand the geometry set up for a bike? I have a lot of questions that I haven’t been able to find answers for.

FRONT
Ideal rake? Is there such a thing? What exactly am I measuring, what happens if there is too much rake to little etc.

BACK
I have the same questions with the back of the bike how do you measure swing arm angle? What is ideal, is there an ideal angle? What happens if it is to flat what happens if there is too much.

I would also like to know a little more about ride height front and back would it be better to raise it up as much as possible lower it down a little bit. Do I use the ride height to make create the proper rake and swing arm angle?

Any help you could give me would be greatly appreciated. Thank you.


Dustin Geiselman



REPLY:

Hi Dustin,

Thanks for the kind words! Glad that these tools have helped you so far and given you a leg up in your racing. I would be happy to put your race pic and a testimonial on the CRST site in the race section!

On to your questions: note that as with SAG settings, rake and trail are arbitrary starting points when buidling a race bike.

There are accepted norms and then you deviate to suit your own personal needs. As always to get something you will give something up, so it os always a compromise.......

Forks:

Rake is ideal at 28 to 29 degrees. Most sport bikes are in this general ballpark and all manufacturers post these numbers in their spec sheets online. The smaller the number the more the bike wants to turn in by itself.

Trail is ideal bove 101-102mm, and again numbers are posted by OEM's. Trail gives mid corner stability and facilitates high cornering speeds.

NOTE: this is why aftermarket triple clamps are manufactured, OEM's provide adjustable steering head pivots etc so you can have low rake numbers with high trail numbers to get the best of both worlds.

Swingarm:
Depends on the engine configuration as to what works 'better' but your rule of thumb is 11 degrees to start. Swingarm angle is critical for side grip and correlates directly to wheelbase length, hence aftermarket shocks having adjustable ride height and some frames facilitating spacers between the shock and frame mount.

Remember that hot pressures are critical too - if the edge of the tire is not up to temp you won't get edge grip anyway!

Hope this helps!! Many thanks and happy holidays.