RT-1 Food For Thought

[Tahitian_Red]

I'm searching for lowering kit for my RT-1, but I starting thinking (always dangerous).  The center of gravity is too high compared to Euro-bikes of the same era and it has too much weight on the back wheel (lengthening the swingarm helped that), but looking at my 2008 YZ450F sitting next to it, the center-line of the crank is much further above a line connecting the two axles and it is carrying weight even higher from ground level.  So, is it all relative?  Will my RT-1 with great suspension (Works shocks and RaceTech emulators) and a longer swingarm handle well against the Huskies, CZ's and Maicos, but just not be able to corner with them, just as a 74.5 Maico should be able to corner under any modern bike?

 

[Freakshow]

thats why they made the frame lowering kits.......

[firko]

Over the years I've raced both lowered and stock framed DT1's and a stock framed DT1 with a lengthened swingarm and know for sure that getting the crank centreline an inch or so lower than the swingarm pivot centreline by lowering the frame rails genuinely helps the bikes 'turnability'. However, I reckon that the single most effective mod you can do to the frame is to lengthen the swingarm 2". Stretching the swingarm seems take a lot of the DT1's notorious 'tankslapper' behaviour and the bike exits corners noticably better.

B
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[Tahitian_Red]

My thinking is this, while a little lower would be better, I'm basically a post-76 bike rider.  The majority of my bikes have a higher center of gravity than any pre-75 bike.  I'm thinking I may not notice it as some test rider that just jumped off '71 Husky or Maico. 

The rules I'm under do not allow for modified frames at this time.  I do not plan to take my Pursang or Phantom with me when I race the RT-1 for the first time.

[firko]

Back in the days when we raced DT1's and RT1's we were limited by our pockets and availability as to what we could do to the suspension. Even though Ceriani and Betor forks were available, they were considered to be pretty exotic and way too expensive. Today however we can dial up eBay and grab a set of cheap Betors out of some Spanish MX'er or even a pair of Ceriani's which are still considered exotic and are still expensive when compared to the almost identical Betors. Even better we can go to YSS or Race-Tech and buy a set of cartridge emulators and trick springs that transform the stock forks (or our Betors or Cerianis) beyond anything we'd have comprehended back in '71. It's the same with shocks, with an ever growing number of firms producing quality shocks that perform better than anything we could have dreamed of a few years ago let alone back in the dark old seventies, our RT1/DT1 rides and handles so much better than the trickest of the trick DT1's from back in 1971.

In a nutshell, I think that the longer swingarm combined with cartridge emulators and deluxe shocks make a bigger contribution overall than lowering the frame but if you can combine the frame kit as well, it really transforms the old Yamahas.

[vandy010]

i raced my RT1 for about 2 yrs with the stock frame and thought it was ok and i just decided to live with it.
it didn't corner too bad, or so i thought, till the back end stepped out then it was just a twitchy mess that i wrote off to old bikes. i had the back end step out real bad over a jump one time and it scarred me enough to decide to do the frame lowering mod.
it really did change the bike for the better.
although as you say your rules don't allow for the mod, it's a shame and it sounds like what you've done so far is about as good as it'll get.
even with the frame mod though, they're still and will always be heavy.
but oooo, that motor....

[firko]

Here's Don Jones thoughts on DT-1 frame mods:

Don Jones said, “The Yamaha DT-1 engine was bulletproof and had good horsepower. For some reason they just didn’t handle right. We changed everything in the world on that bike. Moved the engine up and down, back and forth. Had swing arms short and long. Different length forks and different steering angles. When the kids would come in and say this baby handles good. So we would let other people then try it. That was our measuring stick of what worked and what didn’t. On the first stock DT-1 frames we did add two inches to the frame to lower it for better handling, but we were never happy with that and especially re-welding it back up without being able to treat the weld, and we broke a bunch of those frames also.

The above is an excerpt from an interesting piece on how Don Jones developed the YZ-A from the original DT-1. Here's the link to the full piece...........http://www.wsmchof.com/don-jones-yz-birth.html

[Iain Cameron]

Thats a great link Mark . mmmm an " A to Z " in the shed would be nice . Iain

[Tahitian_Red]

I just read a 1972 Dirt Bike article evaluating the Webco DT-1 lowering kit.  They thought 1 3/4 to 2 inches may have been too much.  They speculate a 1 inch maximum may have been better.

 

[Andrew L]

Does the frame lowering only apply to the dt1 / rt1 or does it help the rt2 rt3 models as well

[vandy010]

Does the frame lowering only apply to the dt1 / rt1 or does it help the rt2 rt3 models as well

they're all the same frame, so yes, it applies to all the DT/RT1,2,3 models