Triumphrat

uzidzit · 02-08-2008

The Suzuki SV650 1999-2007 models, use the same fork springs (basic diameter and length) as the Bonneville, and Thruxton of all model years:

The correct spring rates for street riding based on riders wt.*:
Stock spring rate .75 kg/mm this is correct for a 60lb. rider!
80 lb. rider the rate is .80kg/mm
115 lb. rider the rate is .85kg/mm
150 lb. rider the rate is .90kg/mm
180 lb. rider the rate is .95kg/mm
215 lb. rider the rate is 1.0kg/mm
250 lb. rider the rate is 1.05kg/mm
280 lb. rider the rate is 1.10kg/mm
315 lb. rider the rate is 1.15kg/mm
350 lb. rider the rate is 1.20kg/mm

Correct spring rates for racing:
40 lb. rider the rate is .80kg/mm
70 lb. rider the rate is .85kg/mm
105 lb. rider the rate is .90kg/mm
135 lb. rider the rate is .95kg/mm
170 lb. rider the rate is 1.00kg/mm
205 lb. rider the rate is 1.05kg/mm
235 lb. rider the rate is 1.10kg/mm
270 lb. rider the rate is 1.15kg/mm
305 lb. rider the rate is 1.20kg/mm

* This is based on a standard wt. bike without lightening modifications.

Pick the closest for the rider wt. going down if in the middle of a range if you want a softer ride, and up to the next step, if you ride a little harder.

With no other modifications, use the stock fork oil wt. and level.

Getting the right spring is the first step in improving the front end.

The absurdly low rider rates are listed, to show how under sprung the Bonneville is from the factory!

When using the Suzuki sv650 springs, start by cutting the spacers so that they are about 1/4" above the top of the fork tubes with the forks fully extended. Measure the sag and then shorten the the spacers the amount that the sag needs to be increased. You should look for a sag of about 30-33% of the travel for street riding, or about 25% for racing, and hard charging.

Check back for the next topics: cartridge emulators, fork oil wt., preload adjusters, Brakes, rear shocks, and interchangeable parts that will save you money.

I am trying to build a data base in this blog that will help find interchangeable parts, with other factory, and after market parts to substitute for the factory parts, for economy, and or increased performance.

Pm me with interchangeable parts you have found, and we will see about adding them to the blog, Hopefully it will grow.

This is not to replace any other blogs but will be focused on the above goals.

mecscc · 02-08-2008

Uzi: Glad you decided to get your blog up and running! This is useful info and its good for it to not just get lost. The stuff you are planning sounds great too. Looking forward to your adding that data too.

Congrats!!!!!!!!!

sweatmachine · 02-08-2008

I have sv650 forks on my bike with cartridge emu's in them, the rider I bought them from said he had them set up for his weight, which was I think around 180lbs on a bike that weighs almost 100 lbs lighter than the bonnie. I weigh in at 250lbs so I'm going to dump the fork oil for some 20wt. I think that will firm up the front end quite a bit.

good post!

uzidzit · 02-08-2008

works well for me in my forks, I am using the stock Bonnie forks with cartridge emulators. I run the Emulators at 3 1/2 turns This is kind of firm but I am a big guy. The range you would be in is about two to four, low for street and higher for the track, I assume you want to slow the rebound a Little bit? To get rid of a little front wheel bounce?

I will edit this blog entry just a little I forgot to mention the actual spring size which is 35mm diameter and 340mm long.

There is room in the fork to use a longer spring of this diameter, which could be useful if a spring of greater rate is needed than generally is available, I am planning to add the "How to increase, Spring rates" as a topic for another day.

I picked the SV650 as the model to reference because all the high performance spring sellers know the size of its springs and directly list them on their web sites, this makes ordering easy, and because its spring size is the same as the bonnies when new.

Baltobonneville · 02-08-2008

Uzi, do you know the spring rates for the "standard" Hagons and Icons that many of us have installed?

uzidzit · 02-09-2008

They are however, higher rate across the board.

But here is the longer answer, Those springs are progressive wound and that complicates things a lot. Because their rate is changing at every level of compression, The graph of rate vs compression will look like a curve, and not a straight line.

That is why it gets really hard to tune with them. I don't think I can get a hold of the curve for the Ikon I have sent several requests and have gotten no reply, One of the techs from progressive has promised this information but as of yet I have not received it. The fellow that imports Hagon seems like he wanted to let me know but just did not have the data.

The longer the spacer you use the higher the inital rate and the fully compressed rate.

If there is someone that will donate a spring for some non destructive testing, I will be more than happy to run a test and generate the rate curve for for these progressive springs, and post the results and return the spring at my expense, I would need the spring for about a week. In the mean while I will continue to to try to get a curve from these three makers. If they come through I will post the curves.

This information would help a lot, and allow a little tweaking, by changing the spacer length.

Up Date I got a reply from Progressive and the spring now shows in a pdf form on their web site, their recommended springs rate is.63kg/mm starting to .89kg/mm at the compressed end, the search continues for Hagon and ikon.