Fitting a radial sports tyres to an old Laverda -(by Doug Home)-:
Tyres manufacturers generarly advise to NOT put radial tyres on old tube type
rims, even if the reasons are not always explained with precision. Consequently,
the following article should be considered just as a personal testimony of the author, who uses with other Laverdists radial tyres for years with success, so it cannot
pledge the author or the website responsability. Any rider interested in fitting radial tyres to an old Laverda should ask first to the tyre manufacturers for advices.
If you have been looking at fitting sport compound radial
tyres to your old Lav 18" rims; you may have noticed that you are not exactly
choice. What to do? Well, lets first see what 18" tyres are available and then figure out what we should/could fit.
1. What width 18" radial sports tyres can I fit?
Front: 100 - 110 is fine. Do not go bigger. All the 18" radial fronts are in this range anyway. A 100 - 110 front tyre needs a 2.15 to 2.50 rim so the
standard FLAM rim is ok. The 17" radials seem to start at 120. These will understeer and stand up badly under braking if the bike setup is not modified.
Rear: The smallest radial on the market is 130. This needs a 2.50 -3.00 rim. So the standard FLAM rim is ok.
Read on. A 150 rear needs a 3.00 -3.50 rim. Will be ok on the SFC 1000 rim but not the FLAM rims. If you have FLAMs, you'll have to consider
changing - see below for options.
The maximum size that can go into a 3C swing arm is 150 - 3mm a side clearance. A SFC swing arm will take a 160. If you are thinking of getting a SFC
swing arm and converting it to fit a 3C frame - don't waste your time and money. It is easier and cheaper to make a new swing arm.
Note: The load rating is crucial for the performance and stability of a radial - far more so than a straight bias tyre. This is because a radial is designed to flex
a lot in the sidewall. If you get too "light” a tyre it can flex too much leading to over heating of the carcass, reduced stability and maybe catastrophic failure.
For this reason I will limit my tyre selection to load ratings of +58 front and +66 rear.
Question 2. What width
18" radial sports tyres can I buy?
Sports and the sport/tourer tyres have speed ratings of ZR and V. If you judge that a H is ok for your riding style and habits, stick with a straight bias tyre as
there is a very good 18" range to choose from and you'll avoid all this aggravation and expense.
First let’s get this special case out of the way.
|You can get a Michelin Macadam100 130/70ZR18 63W. Good, it will fit the standard rim. Boing!! Remember +66 rear load rating? This thing is far too light for a Lav. We tried it on three bikes with very different set ups. It flexes badly especially in long high-speed sweepers. It can be settled temporarily by bringing more weight to the inside of the comer and powering on. This collapses it a bit which stops it rippling and weaving. Do this a lot and you'll get increased sidewall heat, loss of grip/handling and maybe catastrophic failure. It's an ok tyre for a Honda 125 commuter.|| |
This is the list as at September 2004. It has a few ZRs and no Vs.
|Avon||AV45 Azaro-ST||110/80ZR18 58W, 160/60ZR18 70W|
|Bridgestone||BT-012SS||110/80ZR18 58W, 150/70ZR18 70W|
|Bridgestone||BT-014||150/60ZR18 67W, 160/60ZR18 70W|
|Bridgestone||Bridgestone BT020||110/80ZR18 58W, 160/60ZR18 70W|
|Metzeler||MEZ 4||110/80ZR18 58W, 160/60ZR18 70W|
|Metzeler||Roadtec Z6||110/80ZR18 58W, 160/60ZR18 70W|
|Michelin||Macadam 100||110/80ZR18 58W, 150/70ZR18 70W, 160/60ZR18 70W|
|Michelin||Pilot Road||110/80ZR18 58W, 160/60ZR18 70W|
|Pirelli||Dragon GTS||110/80ZR18 58W, 160/60ZR18 70W|
That is it. For standard rims
eight fronts and no rears. If you have a SFC1000 or are willing to change wheels,
there are three 150 rears that will fit a 3C
swing arm and nine 160 rears that will fit a SFC1000 swing arm.
As far as sets go, there are two sets of 110 and 150 – the Bridgestone BT012SS and the Michelin Macadam 100, and seven sets of 110 and 160 - Avon,
Bridgestone BT020, Michelin’s Macadam 100 and Pilot Road, Metzeler's MEZ 4 and Z6 and Pirelli's Dragon GTS.
3: If I am going to change wheels why not get 17"?
Ok, I'll deal with the pros and cons of fitting 17" rims: 16"??? – you must be a lost Guzzi reader. The main pro seems to be one of choice.
There is a big range of both V and ZR tyres in 17" as we know. However, most of these are 160s or bigger so you'll have to look at changing the swing
arm if you don’t have a SFC1000. Anything bigger than 160 and you'll be rubbing the chain on the side of the tyre even with a SFC swing arm.
So changing to 17"”is not that attractive.
The cons? I see three.
1- Front tyre profiles. Most 17" front tyres are wider (120s) and have a lower profile (/60) than the 18s. That profile really messes up the steering esp.
under braking – we have tried this on a SFC. You will have to spend a bit of time and money changing the bike setup to fix this if you decide on 17s.
Generally this involves shifting the weight "forward" by lifting the rear up a bit. Setting up like this will show up the limitations of the old fashioned damper
rod forks - like a Cerianis. And so it goes.
2- Keeping the look of the thing: With 18" cast rims, you have a choice of thin spokes and 3 spokes. The 17" only come in 3 spokes - and some of these
are curved in the direction of travel. That is ok if your chain is on the left. If its on the right so you will have to put in backwards. Not a problem until you step
to the side of the bike and see the spoke curves going the wrong way. It looks daft.
|3- Speedo: Fitting a cable
driven speedo and matching it to the ND/Veglia gearing can present some difficulties.
Tyre profiles can be worked around by|
looking at the circumference of the tyre. There is a guy in Woollongong who makes a nifty little switch calibrator that changes the frequency into a digital pod.
Question 4: What do I have to do to fit
1. Just fit the things.
|Ok with the front but not really recommended for the rear. This is a Macadam 150 on a standard 2.50 Lav rim. It fits but it’s not really smart – that why I did it. Firstly, for a radial to work as a radial the sidewalls have to be able freely flex. The manufacturer’s recommended installed tyre width is the width at which the sidewall can flex enough to get the right contact patch on the ground especially during cornering. This is 152mm for the Bridgestone BT010 and 158mm for the Macadam100. Squeeze either on to a 2.50 Lav rim and you'll get 128mm. So you'll get the benefit of a softer rubber compound (maybe) but not the radial. The second is a safety issue - the thing might peel of the rim. I fitted both the Bridgestone and the Macadam and took it fairly frequently to +200kph or so and they didn't but...….What did happen though was small cracks appeared about mid- spoke at three places. I would dissuade you from fitting big radials on the standard rear rim – one silly person is enough.||
2. Keep the FLAM fronts and change the rear to a 3.00 - 3.50 18".
There are five possible ways to do this.
First possible - buy spare SFC rear rim - seen any hen's teeth lately? If you own a SFC, the choice comes down to a pair of Bridgestone BT012SS or a
pair of Michelin Macadam 100s. No choice really - get the BT012SSs. If they are an upgrade on the venerable BT010; they will be great and the BT010
was/is so far ahead of the Mac 100 as to make comparisons laughable.
possible - there are other 3.00 - 3.50 18" rear rims about - early 1980s Kawasaki’s
or Suzuki’s GS or Kat as examples. These would be a lot cheaper and more available
than a SFC rim. I have not priced this. Fitting them would involve first reversing
the rim then cutting down the sprocket carrier to get the chain to line up and
then making up spacers and (maybe) an axle. Now you'll need to fit a rear caliper
- so a bracket to fit the F08 Brembos or a new caliper. |
See below for some estimated costs from my experience.
|Third possible - buy a 3.50 Astralite
or Marvic rim. These are nice rims and they look good in the bike. Some Motodds
have them in. Can be hard to find. |
I found a few secondhand pairs on the web (Shipley, West Yorkshire) at ridiculously low prices - A$260 for a pair of Astralites with tyres and A$770 for a pair of Marvics! Whether they are still available or their condition?? If I were starting out converting my thing I would look at them.
Will need calipers, bracketry and maybe axles and discs as well.
|Fourth possible - buy a
Talon hub and an Excel 3.50 - 4.25 rim and lace them together. I like this alternative
as I think a wire wheel suits these bikes. This is a motard setup ie: 160kg wet
- for the Lav weight, go for the chrome steel big dimple rims. |
Cost for a complete wheel would be around A$800. Then you'll need calipers, axles and a speedo. If you wanted a matching pair, Excel has 2.15 fronts as well. This is quite a cost effective alternative and you'll end up with a very light unsprung weight wheel (esp. when compared to the Yamaha 17" 3 spoke lumps) that will look really good and be fairly unique.
I would research the spoke design and materials fairly closely and get them laced by a professional.
- fit a late 1980s - early 1990s 3.50 or 4.00 18" rim. There are 2 options here.
You can get a thin spoke or a 3 spoke rim. |
The thin spokes went out of fashion around the early 1990s.
About the same time as the 17' rims started to appear.
There are some 18" 3 spoke wheels about but they are fairly rare - the 1992 GSXR 750 from memory.
The thin spoke GSXR rim (thanks to SFCPiet for alerting me to them) look fairly similar to the SFC 1000
rim and they are not directional so when you fit the rear in backwards, it still looks ok.
They looked like they belonged - some people even thought they were Lav rims.
"Where did you get a 4.00 Lav rim?"
The good other thing was the standard axle fitted.
| ||Anyway, a 3.50 or 4.00 rear out of a 1989 GSXR 750/1100 with a 220mm disc will set you back about A$400. A 2 spot rear caliper A$125. Now you'll need to make up a caliper bracket, torque rod and braided lines plus fit a better rear master cylinder to make it look like this, another A$350. Then you'll have to start fiddling with spacers to get the standard Lav axle to fit. You'll have to machine the sprocket carrier down to get the chain to line up. Add another A$150. While you are doing this, machine a new sprocket land on the carrier - don't break through into the bolt recesses. Then get a blank sprocket and machine and drill it to suit the hub. Add another A$100 for that. Total excluding the tyre A$1200.|
Change the fronts and the rear to a matching pair. Same possible as above.
You'll have as much luck getting a SFC front as you will a rear. so I'd look at
Jap cast rims. If you do decide to change both wheels - a front with disc will set you back A$400-600 depending on the year. Make sure the disc buttons
clear the inside of the stanchions or you will end up with embarrassing grinding noises. For a Ceriani, the max measurement across the disc buttons is 146mm -
that will give you 1mm clearance a side so make the spacers up accurately.
|You'll need some calipers to go with
it. A$300 for a pair of good 4 spots. |
The caliper brackets will set you back A$250.
Some braided lines and an applicable master cylinder with handgrip, add another A$250.
New pads and rebuild kits for the calipers, another A$250.
Now you'll need two spacers to fit the wheel in. Use the original Lav axles.
You can fit a cable driven speedo to a GSXR wheel - like this from SFCPiet.
Some attention will have to be paid to the speedo gearing so that
the ND ouijia boards do not start indicating you are getting 260kph on the way
Another way is to fit a dirt bike speedo/odometer - like the Huskys and KTMs have on or just a plain pushbike one does the job.
|This was all too hard for me and I as I had just trashed my ND pod whilst throwing the thing up the road, I went digital. A digital/analogue pod of a GSXR600 A$450. Wiring it into a Lav loom was relatively easy once I had a Suzuki wiring diagram. It helped that I was running an IIS ignition as I took a feed from the coils to the digital analogue tacho. The analogue speedo had to be calibrated as it was set up for a 17" wheel so a little switch calibrator (A$ 100) got it all accurate. Drive the speedo of a magnetic pickup reading of back disc bolts (A$150) The thing just above the caliper sticking out of the hanger bracket in the jpeg above. If you go this path, you'll need at least 10 magnetic pickup points to get the thing within calibration range – put in five chrome socket head screws and the thing counts the gaps to get to ten.|
| ||The finished article. Total cost about A$3500.|
last option is to fit a 3 spoke 2.50 fronts and 4.00 - 4.50 rear 17" rims.
If you can cope with looking at the curved spoke ones running backwards,
the GSXR 750 3 spokes are the best/easiest. The Yamaha - TRX/R6 or R1 will go in the front but will need some significant machine work to get the rear in.
Cost and work required would be pretty much as for the 18" except you'll need to make up 2 new axles - add another A$300. Total = A$3800. Then you'll
have to re-tune the bike suspension setup - see above.
There you go. Your money - your
Doug Home. firstname.lastname@example.org